What does it look like?
Portuguese millipedes belong to a group of invertebrates called Myriapoda. They have a many-segmented, smooth cylindrical body ranging in colour from black/grey to light brown. When mature, they may be up to 45mm long with as many as 50 body segments, each with two pairs of legs. When disturbed, they commonly curl into a tight ball or may thrash around.
Portuguese millipedes feed on decomposing organic matter such as leaf litter, decaying wood, and moss. In gardens they will commonly be found in and around compost bins, or areas where there is a thick layer of mulch or leaf litter, as these areas provide shelter, moisture, and food. However, Portuguese millipedes can survive without food and water for many weeks.
They are attracted to lights and are often found in well-mulched garden beds close to houses. Portuguese millipedes reproduce in autumn and early winter – depending on seasonal rain - and are most noticeable at this time as they can gather in large, mobile numbers. The female millipede lays around 200 eggs in the soil, emerging as juveniles six months later. A re-emergence after the first spring rains is common.
Why is it a problem?
Portuguese millipedes can be a nuisance, posing no risk to human health. They are not known to have any negative environmental effects.
However, particularly following periods of heavy rainfall in autumn and spring, they can invade homes and buildings in large numbers. If they are squashed, they can release a pungent yellow secretion which may stain carpets and clothing. They do not breed indoors and will usually die once inside.
Control methods
There are some options available to reduce millipede numbers but no single solution:
- Keep compost and mulched areas - suitable habitat and sources of food - as far away from your house as possible
- Millipedes cannot cross smooth vertical surfaces, so try installing barriers such as plate glass, smooth vinyl or polythene tape in an upright position around the base of the house, below doorsteps or under window ledges. Any barrier should be continuous with no breaks (unless under doorways) and kept free of bridging vegetation.
- Set light traps along any outside wall where millipedes are entering. This wall can also be treated with an appropriate insecticide. Lights can also be set up in the garden to lure millipedes away from dwellings. It’s recommended that external lights are turned off when not needed, and affected residents should limit the light that escapes through their blinds and windows.
- Use sprays containing the active ingredient bifenthrin under hiding places (e.g. wooden sleepers, pot plants and decorative garden objects) as well as surrounding areas. Sprays can also be applied to ground surfaces and walls. Be careful when using pesticides around animals - ensure you follow all label precautions.
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